Percussion drill bits for rock perforators may have a frontal face covered by a plurality of hard-metal studs, several such studs being arranged in a group. The resulting groups maybe at a distance from each other at least in circumferential direction and separated from each other by channels for the circulation medium. Further, the bit may be provided with at least one axial channel opening into the channels and located approximately centrally within the frontal face, serving as an outlet for the circulation medium.
Such a drill bit is known for instance from German open application DE OS No. 27 33 300.
Indeed, in the case of this already-known two-part drill bit, cutting inserts, for instance in the shape of hard-metal studs are provided in groups, whereby the groups are separated from each other through circulation-medium channels running radially, respectively in given cases, slightly curved in the direction of rotation.
The studs are indeed arranged in a multiple setting on an island, protruding with respect to the circulation-medium channels so that larger lumps of detritus can get stuck between the studs. This results in a relatively long drilling time for corresponding advances, because these lumps must first be comminuted before they can be evacuated by the circulation-medium through the circulation-medium channels. The circulation-medium channels do not serve for the exhaust gas evacuation. Neither do they help in the evacuation of the detritus, this evacuation being performed solely by the exhaust gas. Furthermore, the studs arranged in this manner can be reground only with difficulty, since the neighboring studs mutually impede their regrinding.
For the mounting of such drill bits to rock perforators it is common, in the case of the so-called sinker drills, to introduce a slotted shaft in a holding member. Thereby the drive operates counterclockwise. Alternatively it is also possible, in the case of surface drills, to provide the shaft with an inner threading, which can then be threaded to a nipple. This embodiment turns clockwise.
The individual arrangement of studs protruding from the main body of the drill bit is known from the German open application No. 26 33 779. This arrangement facilitates the regrinding of the studs, but obstructs the evacuation of the detritus. Moreover, larger lumps of detritus can continue to get stuck between the studs.